Peptide Nomenclature Guide

Symbols and structures for amino acids

Common (“proteinogenic” or “coded”) amino acids have a three-letter symbol and are also represented by a one-letter symbol. Uncommon amino acids also have three-letter symbols and can be represented by the one-letter symbol “X”. The tables below list the symbols and abbreviations used in our website and literature.

Table 1. Common Amino Acids

Key -  Acidic    Basic    Non-polar (hydrophobic)    Polar (uncharged)

Amino acid Three-letter symbol One-letter symbol Chemical structure
Alanine Ala A Alanine
Arginine Arg R Arginine
Asparagine Asn N Asparagine
Aspartic acid Asp D Aspartic acid
Cysteine Cys C Cysteine
Glutamine Gln Q Glutamine
Glutamic acid Glu E Glutamic acid
Glycine Gly G Glycine
Histidine His H Histidine
Isoleucine Ile I Isoleucine
Leucine Leu L Leucine
Lysine Lys K Lysine
Methionine Met M Methionine
Phenylalanine Phe F Phenylalanine
Proline Pro P Proline
Serine Ser S Serine
Threonine Thr T Threonine
Tryptophan Trp W Tryptophan
Tyrosine Tyr Y Tyrosine
Valine Val V Valine

Table 2. Uncommon Amino Acids

Three letter symbol Amino Acid
Aad 2-Aminoadipic acid (2-aminohexanedioic acid)
Aan α-Asparagine
Abu 2-Aminobutanoic acid
Aca 2-Aminocapric acid (2-aminodecanoic acid)
Agn α-Glutamine
Aib α-Aminoisobutyric acid (α-methylalanine)
Apm 2-Aminopimelic acid (2-aminoheptanedioic acid)
App γ-Amino-β-hydroxybenzenepentanoic acid
Asu 2-Aminosuberic acid (2-aminooctanedioic acid)
AzaGly 2-Azaglycine
Aze 2-Carboxyazetidine
Bal β-Alanine
Bas β-Aspartic acid
Bly 3,6-Diaminohexanoic acid (β-lysine)
Bua Butanoic acid
Bux 4-Amino-3-hydroxybutanoic acid
Cap γ-Amino-β-hydroxycyclohexanepentanoic acid
Cha 3-Cyclohexylalanine
Cit N5-Aminocarbonylornithine
Cya 3-Sulfoalanine
Dab 2,4-Diaminobutanoic acid
Dap Diaminopropionic acid
Dpm Diaminopimelic acid
Dpr 2,3-Diaminopropanoic acid
Dsu 2,7-Diaminosuberic acid (2,7-diaminooctanedioic acid)
Edc S-Ethylthiocysteine
Ggu γ-Glutamic acid
Gla γ-Carboxyglutamic acid
Glc Hydroxyacetic acid (glycolic acid)
Glp Pyroglutamic acid (Pyr) (pGlu)
Har Homoarginine
Hcy Homocysteine
Hhs Homohistidine
Hiv 2-Hydroxyisovaleric acid
Hse Homoserine
Hva 2-Hydroxypentanoic acid
Hyl 5-Hydroxylysine
Hyp 4-Hydroxyproline
Igl α-Amino-2-indanacetic acid
Iva Isovaline
Lac 2-Hydroxypropanoic acid (lactic acid)
Maa Mercaptoacetic acid
Mba Mercaptobutanoic acid
Mhp 3-Hydroxy-4-methylproline
Mpa Mercaptopropanoic acid
Nal 3-Naphthylalanine
Nle Norleucine
Nphe N-Benzylglycine
Nty Nortyrosine
Nva Norvaline
Oaa ω-Amino acid
Oic 2-Carboxyoctahydroindole
Orn Ornithine
Pen Penicillamine (3-mercaptovaline)
Phg 2-Phenylglycine
Pip 2-Carboxypiperidine
Pmp β,β-Cyclopentamethylene-β-Mercaptopropionic acid
pSer Phospho-L-serine
pThr Phospho-L-threonine
pTyr Phospho-L-tyrosine
Pya(4) 3-(4-Pyridinyl)-alanine
Sar Sarcosine (N-methylglycine)
Spg 1-Amino-1-carboxycyclopentane
Sta Statine ((3S,4S)-4-amino-3-hydroxy-6-methylheptanoic acid) (AHMHA) 
Thi 3-Thienylalanine
Tac 2-Tolylaminophenylcabonyl ([(2-Methylphenyl)amino]carbonyl)
Tic 3-Carboxyisoquinoline
Tle 3-Methylvaline
Tml ε-N-Trimethyllysine
Tza 3-Thiazolylalanine
Und Undefined
Wil α-Amino-2,4-dioxopyrimidinepropanoic acid

Table 3. Substituents

Abbreviation Substituent
Ac Acetyl
Bn Benzyl, Bzl
Bz Benzoyl
For Formyl
Me Methyl
Myr Myristoyl
Z Benzyloxycarbonyl